1. Field of the Invention
This invention relates to a semiconductor light emitting device, its manufacturing method, and an optical recording and/or reproducing apparatus. More particularly, the invention relates to a semiconductor light emitting device using II-VI compound semiconductors, and a manufacturing method thereof, and an optical recording and/or reproducing apparatus using the semiconductor light emitting device as its light emitting device.
2. Description of the Related Art
For purposes of realizing higher densities and higher resolutions of optical discs and magneto-optical discs, there is a progressively strong demand for semiconductor light emitting devices such as semiconductor lasers, light emitting diodes, etc. for emitting blue to green light, and studies are being made for realization of such devices.
Most hopeful materials for manufacturing semiconductor light emitting devices for emitting blue to green light are II-VI compound semiconductors using group II elements, such as Zn, Cd, Mg, Hg and Be, and group VI elements, such as S, Se, Te and O. Especially, a quaternary mixed crystal, ZnMgSSe, is known as a material which can be crystallographically grown on a GaAs substrate excellent in crystalline property and readily available and is therefore suitable for forming cladding layers, optical guide layers upon manufacturing semiconductor lasers for emission of blue light, for example, using the GaAs substrate (for example, Electronics Letters 28(1992) p.1798).
A typical conventional method for manufacturing semiconductor light emitting devices using II-VI compound semiconductors, in particular, semiconductor light emitting devices using ZnMgSSe layers as cladding layers, was to sequentially grow an n-type MgSSe cladding layer, active layer, p-type ZnMGSSe cladding layer, active layer, p-type ZnMgSSe cladding layer, p-type ZnSe contact layer on an n-type GaAs substrate via a buffer layer by molecular beam epitaxy (MBE), thereafter form a p-side electrode on the p-type ZnSe contact layer, and form an n-side electrode on the bottom surface of the n-type GaAs substrate. In these semiconductor light emitting devices, however, it was difficult to bring the p-side electrode into ohmic contact with the p-type ZnSe contact layer because of a difficulty in increasing the carrier concentration of the p-type ZnSe contact layer.
To overcome the problem, another technology was proposed, which grows a p-type ZnSe/ZnTe multiquantum well(MQW) layer on a p-type ZnSe contact layer, additionally grows thereon a p-type ZnTe contact layer readily made with a high carrier concentration, and further grows thereon a p-side electrode, in particular, a Pd/Pt/Au p-side electrode, so as to improve the ohmic contact characteristics. Actually, continuous oscillation at a room temperature has been realized with a semiconductor laser which employs the above-mentioned contact structure of the p-side electrode in a ZnSe/ZnSSe/ZnMgSSe SCH structure (Separate Confinement Heterostructure) using a ZnCdSe layer as the active layer, ZnSSe layer as the optical guide layer, ZnMgSSe layer as the cladding layer (for example, JPN. J. Appl. Phys. 33(1994) p.L938).